Displays with large-sized screens, such as rear-projection-type displays, are required to have greater viewing angles as compared to displays with small-sized screens because it is a common manner that many people view, at the same time, the images displayed on the large-sized screens. For example, a projection television, a rear-projection-type display, has a transmission type screen (rear projection screen) on which imaging light emitted from a light source is projected. Generally, this transmission type screen comprises a Fresnel lens sheet, a lens member, for deflecting the imaging light projected from the light source so as to make it parallel or nearly parallel light (hereinafter collectively referred to as nearly parallel light), and a light-diffusing member for diffusing the nearly parallel light so as to make the viewing angle greater.
In the meantime, there has been known, as the above-described light-diffusing member, a refraction-type lenticular lens member in which cylindrical lenses extending in one direction parallel to the sheet plane of the light-diffusing member (for example, in the vertical direction when incorporated in a display) are juxtaposed in another direction nearly perpendicular to the above one direction (for example, in the horizontal direction when incorporated in a display). Another known light-diffusing member is a total-reflection-type lenticular lens member having a diffusing-part base in which a plurality of grooves extending in one direction parallel to the sheet plane of the light-diffusing member have been made so that they are juxtaposed in another direction nearly perpendicular to the above one direction, and light-absorbing parts formed by filling the grooves with a low-refractive-index material including dark-colored particles. In the total-reflection-type lenticular lens member, the diffusing-part base has, between the grooves, unit lens parts having nearly trapezoidal cross sections, and the unit lens part—light-absorbing part interface totally reflects at least a part of incident light so as to diffuse transmitted light.
For example, as described in Japanese Patent Laid-Open Publication No. 2004-4148, a lenticular lens member of the above-described total reflection type comprises a light-diffusing part having unit lens parts (lens elements) whose cross sections are nearly trapezoidal, and light-absorbing parts between the unit lens parts, having wedge-like cross sections. The upper bases of the unit lens parts form the light-outgoing surface (light-emergent surface) of the light-diffusing part, and on the light-diffusing part is formed a pattern (BS pattern) for absorbing stray light, extraneous light, and so forth, which looks like stripes in black when viewed from the light-outgoing side (light-emergent side). The light-absorbing parts constitute the black portions of the black-stripe pattern.
In parts of the light-diffusing member where the upper base and the lower base of each unit lens are seen superposed when viewed along the direction perpendicular to the sheet plane of the light-diffusing member, light vertically entering the sheet plane of the light-diffusing member is transmitted as it is and emerges from the plane of emergence. However, in the other parts, light vertically entering the sheet plane of the light-diffusing member is totally reflected from the unit lens part—light-absorbing part interface, and then the reflected light is refracted by the interface between the upper bases of the unit lens parts and a medium layer formed on the upper bases and emerges from the light-diffusing member. Further, in this total-reflection-type lenticular lens member, since an ultraviolet-curing resin composition containing dark-colored particles is used to form the light-absorbing parts, the light-absorbing parts function as black stripes and can therefore enhance the contrast of an image to be projected on a transmission type screen.
FIG. 10 is a schematic sectional view showing a lenticular lens member of total reflection type, and FIG. 8 is a flow sheet showing a process for producing the lenticular lens member. As shown in FIG. 10, a total-reflection-type lenticular lens member 101 comprises a substrate 102, a light-diffusing part 103, an adhesive layer 104, and a supporting plate 105. The light-diffusing part 103 has a diffusing-part base 103a having a large number of nearly V-shaped grooves 106 tapered down to a point toward the substrate, and light-absorbing parts 103b formed by filling the grooves 106 with an ultraviolet-curing resin composition containing colored particles. The portions between two adjacent light-absorbing parts 103b and 103b of the diffusing-part base 103a form the above-described unit lens parts 108. In the production of such a total-reflection-type lenticular lens member 101, an ultraviolet-curing resin composition 113 for forming the diffusing-part base is, as shown in FIG. 8, supplied between a forming roll 111 having, on its periphery, nearly trapezoidal concavities for making the nearly V-shaped grooves, and a substrate 112 to be fed to the forming roll 111, while rotating the forming roll 111. The ultraviolet-curing resin composition 113 is then exposed to ultraviolet light emitted from a UV lamp 114 so as to form the diffusing-part base 103a with grooves, thereby obtaining an intermediate member 115 having the diffusing-part base 103a and the substrate 112. Thereafter, this intermediate member 115 is separated from the forming roll 111, and the grooves in this member are filled with an ultraviolet-curing resin composition 116 including colored particles. The ultraviolet-curing resin composition 116 is then exposed to ultraviolet light from a UV lamp 117 so as to form the light-absorbing parts 103b, thereby obtaining the light-diffusing part 103 having the diffusing-part base 103a and the light-absorbing parts 103b. In the subsequent step not shown in the figure, a supporting plate 105 is laminated to the light-diffusing part 103 with an adhesive, thereby obtaining the light-diffusing member 101. In this production process, in order to fill the grooves in the intermediate member 115 separated from the forming roll 111 with the ultraviolet-curing resin composition 116, the resin composition is scraped off with a doctor 118 from the upper bases 109 of the unit lens parts 108 into the grooves.
However, in the above-described total-reflection-type lenticular lens member, non-uniformity in stripes brought about by covering (overlaying, overlapping, blushing, bronzing) is occasionally observed on the light-transmitting portions, i.e. the upper bases of the unit lens parts, between the BS pattern. In more detail, in the process for producing the total-reflection-type lenticular lens member, shown in FIG. 8, when the ultraviolet-curing resin composition is scraped off with the doctor 118 from the upper bases 109 of the unit lens parts 108 into the grooves, the colored-particle-containing resin 110 that has slipped through the gaps between the doctor 118 and the light-transmitting portions between the light-absorbing parts 103b and 103b (the upper bases 109 of the unit lens parts 108) can remain on the light-transmitting portions in order to cause so-called “covering”.
If the lenticular lens member on which covering has occurred is used in order to make a transmission type screen, since transmittance of light is disturbed by the colored particles remaining on the upper bases 109 of the unit lens parts 108, the covering is perceived by viewers as “non-uniformity in stripes”, which is a phenomenon that the upper bases 109 of the unit lens parts 108, constituting a BS pattern, seem non-uniform in width. The lenticular lens member on which covering has occurred thus brings about non-uniformity in stripes, resulting in decrease in the product yield of lenticular lens member.
Especially in the recent rear-projection-type displays, light sources of single tube type (hereinafter referred to as “single light sources”), using LCDs (Liquid Crystal Displays) or DLP (Digital Light Processing), have come to be used in order to meet the demand for digital, high-definition, compact displays. Although such rear-projection-type displays using single light sources are advantageous in that they can more sharply display still images and letters by means of pixels display, pixel display being a characteristic feature of this type of displays, they are disadvantageous in that the above-described non-uniformity in stripes that has conventionally been not so noticeable becomes noticeable.